1. Field of the Invention
The present invention relates generally to non-acoustic optical pressure sensors, and specifically to an array of non-acoustic optical pressure sensors for measuring a pressure at multiple locations along the path of the array.
2. Description of Related Art
In the field of reduced size pressure sensors, it is well known to use piezoresistive or capacitive readouts to measure a pressure. In the case of piezoresistive pressure sensors, a diaphragm is exposed to the applied pressure, and the mechanical strain on the diaphragm is measured to determine the amount of pressure acting on the diaphragm. Sensing the state of the mechanical strain in the diaphragm possesses a number of problems. For instance, this type of sensor has a large cross-sensitivity to packaging stress, which may limit the accuracy of the sensor. Furthermore, the resistive elements tend to be temperature sensitive at high temperatures rendering high-temperature applications to also be inaccurate.
Capacitive pressure sensors use a variable-gap capacitor positioned between a diaphragm and an adjacent second plate. As pressure acts on the diaphragm, the amount of deflection of the diaphragm is measured using the capacitance of the variable-gap capacitor to determine the pressure acting on the diaphragm. These pressure sensors also have numerous disadvantages. First, electricity is required to operate these sensors to obtain the required measurements. In some situations such as at remote locations requiring transmission over large distances, it is not convenient or plausible to supply a pressure sensor with electricity, so these types of pressure sensors may not always be readily utilized. Also, besides tending to be sensitive to packaging stress, they tend to be inaccurate in high-temperature applications due to the effects of temperature on their readings. Electrical sensors require electrical contacts formed of a conductive material to be attached to the sensor, which limits the possibilities for the type of material used in forming the contacts. Thus, in extreme environments, such as highly corrosive environments, it can be difficult and expensive to manufacture a pressure sensor having electrical contacts with the desired sensitivity while also being resistive to the corrosive environment.
Many of the current pressure sensors which are designed to be very accurate are extremely expensive. For instance, current pressure sensors using a quartz resonant frequency device, where the resonant frequency is a function of the pressure applied on the sensor, have a one foot depth accuracy at 0.5 psi. These resonant frequency pressure sensors are expensive and large. This makes them unsuitable for applications having a limited space.
In order to reduce the detrimental effects associated with electrical pressure sensors, contactless optical pressure sensors have been utilized to minimize the effects on the sensitivity of the pressure sensors by severe environments and elevated temperatures. Such optical pressure sensors utilize the interference phenomena on a wavelength of light to determine the pressure acting on it. The wavelength of light is transmitted to the optical pressure sensor, wherein a pressure-sensitive mirror is positioned within an interferometer. As the position of the mirror is changed by the pressure acting on it, the gap within the interferometer changes, causing the interference of the wavelength of light within the interferometer to change. The pressure is determined as a function of the interference by comparing the interfered light signal with a predetermined value. However, noise and losses in the light signal occur when the wavelength of light is transmitted over large distances. The interfered light signal being compared with the predetermined value is not the identical signal output by the sensor, due to the associated losses and noise occurring in the signal. Inaccurate pressure measurements can result from this type of pressure sensor.
There is a need for a nonelectric and contactless pressure sensor which does not suffer from the detrimental effects associated with prior pressure sensors requiring electrical connection. Moreover, there is a need for an extremely accurate, compact optical pressure sensor which is not affected by losses associated with transmitting the optical signal.